drahardja, (edited ) #TodayILearned that phase-detection #autofocus is fast and accurate, but not precise—the resulting focus when you hit that AF button is a tiny bit sloppy. When that AF beep is heard, your focus will be ever so slightly front or back of the actual focus point. I’ve seen evidence on my lenses that that where you left your focusing ring the last time affects whether the next autofocus is front- or back-focused.
This means that you should never simply take the first number that Automatic AF Fine Tune gives you. Instead, take a dozen or more readings and average them out to get a feel for your lens’s focus bias, then manually adjust the fine-tune setting. Take a few photos of a sharp, stationary target, and pixel-peep until you get the setting about right. If you’re like me, you’ll get three super sharp shots out of four, with the last one just a bit soft.
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